Ion transport plays an essential role in the maintenance of lens volume and transparency. The long-term goal of this research is to produce a detailed model of lens ion transport that could be used to understand the mechanisms of some types of cataracts. The model will require the details of the individual ion transport processes and their control in each of the cell types in the lens. Using a combination of cell culture and patch technology it is possible to look at the molecular details of conductive ionic transport pathways. Recent experiments on lens epithelial cells have identified three main types of potassium conductances: 1) a delayed rectifier, 2) an inward rectifier and 3) a calcium-activated potassium conductance. It is the hypothesis of this grant that the lens inwardly rectifying potassium conductance functions in setting resting voltage and perhaps buffering extracellular and recycling intracellular potassium. The inward rectifier may also be involved in the process of fiber cell formation. It is the primary objective of this grant to test this hypothesis and characterize the biophysical properties and physiological control mechanisms of this inward rectifier. Biophysical characterization will include description of gating and permeation properties. Measurements of gating will address the issues of allosteric control of the channel by potassium and the mechanism of rectification. Permeation studies will be aimed at finding and characterizing blockers for the channel. Experiments are included that will examine the molecular basis of second messenger control of the inward rectifier and determine if any of the known primary messengers that control inward rectifiers in other tissues or that control lens potassium conductance have effects on the lens inward rectifier. The role of the inward rectifier in setting resting voltage will be determined using blockers and the potassium dependence of the current. Measurements of the biophysical properties and cellular distribution within the lens will be used in assessing the role of the inward rectifier in other functions.